Apparatus for tracing curved lines



y 2, 1939- D. J. WITHERSPOON 2,156,417

APPARATUS FOR TRACING CURVED LINES Filed May 20, 193' 2 Sheets-Sheet lINVENTOR '3 David J IVz'lherspoon ATTORNEY D. WITHERSPOON APPARATUS FORTRACING CURVED LINES May 2, 1939.

Filed May 20, 1937 2 Sheets-Sheet 2 ATTORNEY Patented May 2, 1939 UNITEDSTAT-ES PATENT OFFICE David John Witherspoon, New York,,Nj.-.Y., .asrsignorto Bee-K0 Company, a corporation of New York Application May .20,1937, Serial No. 143,680

1 Claim.

This invention corn-prisesnovel mechanism'tor tracing elliptical. andother outlines which shall have a predetermined curvature ofmathematical exactness.

The preferred form of apparatus embodying my invention is primarilydesigned to trace the outlines of ellipses of different predetermineddimenions, with axes and foci having given locations, by means of amarker carried by a movable or floating member supported byadjustablespaced-apart pivots which are caused to simultaneously reciprocate alonglines at right angles one to the other and parallel to-and overlying theaxes of the desired ellipse. Such rotation causes said floating memberto complete one revolution about constantly shifting axes perpendicularto the plane in which-said member has its movement of translation, ororbitalmotion. If, then, a marker lies in aplane in whichthe axes ofbothivots also lie and outside 'of' the space between them, an ellipse willbe traced.

The best construction for such apparatus embodying my invention atpresent known tome is illustrated in the accompanying two sheets ofdrawings in which Fig. 1 is a plan viewof the apparatus in position upona sheet oidrawing paper or other plane surface on which the curves aretobe traced.

Fig. 2 is a cross section on a vertical-plane'on line 22 of Fig. 1. Inthis view the apparatus is shown as equipped with a lead for tracing thecurved line.

Fig.3 is anenlargeddetail elevation of one end of the-mainframe,theright hand end as shown in 1, partsbeing shown in-section.

Fig. 4 is an enlarged detail elevation of the lead carrier-shown in Fig.2, but looking at the same f-rom'the rear of Fig. 2.

Fig. 5 is a similar detail of the carrier equipped with a pen fortracing the lines.-

Fig.6 is'a detail plan in section of the carrier for .themarker taken online 6-ii'oi Fig. 2, and

Fig. '7 is adetail side elevationof amodifioation in which the marker ismounted on the other-end of the-rod 22,. which is assumed to have beenshoved to :the left; looking, at Fig. 2, for this purpose.

Referringtothe drawings,the apparatus therein shown comprises the endcastings :i i. l i, which may ibeiheldby thumb tacks 23; 23, on thedrawing board or clamped thereto, said castings being rigidly.;.connected :together bythe parallel rods t,-a4,&which serve :asguidesfor the carriage 3 :sliding .fr'eelyzthereon. The .minor axis .oftheellipse to tbeadrawn will lie vbelowrand between said rods sitionsthereon by thumbscrewiilc ,Said clamp maybe supported on a. foot] member=19 (Fig 2) which is adjustable-enrod:- ZZ. which in; turnis adjustable.in.:9.' Thewheel. 29:;(whic ,may in some embodiments .of. my inventionbereplaced by some other anti-friction device), isjpurnaled in IS andS1ld6S.OI',;I'O11S,:O1'1 thesurfaceofthe pa per. Pen-3 t or lead. l and:itsholder are-fialilfi-fid Ion the end of. rod :22 which. isadjlletable endwise i n mp m er eand can .be c amped in admsied positionby setscrew t3. Said;. c lamp is :pivotally connected .at.W- (Fig- 1)-to. the apex of -the straight line motion..systern; .of llnkS 8,- 8b,'8;, 8d, 89. The angle apexof: link pair 8e, 8 has a fixed pivotX'carried by onepf, the castings -;i i, I i, (Fig. 3).. Theangle.apexofpairgt ,C,-(Fig, 1) is pivotally connected at Y- to the end ot, linlg-B; which swingsfreely abouta fixed point -Z. (Fig. 1-) also carried byII.

This straight .line .motionnneeha new per so, having :beemused ,for; dra

. gee ain curved lines bymountin zitein a different way from that hereshown. and. placing-a marker at one of its pivoted -joints..-, {But-"its.use-to compel motion of a member connectedsto its;=pi vot along astraight line .at rightaanglesto that pass.-

.of guides 4, .4,;.outsideof the orbit .of any marker carried .by therevolving flat barj. or. red ;;2 .,and outside the path of other movingparts,; thus simplifying thewhole supporting;. construction. Thefunction. .of .the stra tlin otionm ch nism is .-to. compel pivot W to.,move always and l only in a path indicated by broken line L L in Fig. lwhich extends across and at right angles to the line of guides i, 6.This line of travel LL is also the major axis of the ellipse to be drawnwhen the marker I (Fig. 7) or SI (Fig. 5) is carried at that end of themovable member formed by parts 2, 5, 6, i, ii and 22, on which it isshown as being mounted in Figs. 1 and 2 of the drawings.

I 3 (Fig. l) is a tension spring which is used to maintain the straightline motion linkage under light strains all in the same direction at allits joints at all times so as to take up any slack therein. Otherwisewatchmaking precision would be required in fitting all the six pivotjoints therein included to prevent the links 8 to Br from shiftingslightly in their relative positions under reversals of operatingstrains.

38 is a pointer adjustably mounted in the lower part of clamp 53 in linewith the axis of the pivotal connection W to the straight line motionlinkage. Consequently, this pointer will always travel along the majoraxis of the ellipse when the parts are in motion and a marker located onmember 22 as shown in Fig. 2. It is prevented from sticking into orscratching over the paper 25 by the anti-friction support is for thelefthand end of rod 22 (looking at Fig. 2) previously described.

In the preferred construction of carrier for the marker shown in Figs.2, 4 and 5 there is a downwardly projecting spindle 32 on the righthandend of rod 22 (looking at Fig. 2) on which the block 33 is adjustablymounted, being held in position thereon by setscrew 2G (Figs. 2 and 6).Block 33 is also perforated to receive the adjustable supporting member35 which is held in position by setscrew 35 and has its lower endrounded so as to run smoothly over the paper 25 on which it rests. 36 isa swinging member hinged at 37 to block 33 and carrying at its free endeither the pencil I of Figs. 2, 4 and 6, or the pen 3i of Fig. 5. Anupwardly projecting spring finger 38 is supported on block 33. andprovided with a small projection 39 adapted to register with a companiondepression in the side of the member 36 when the latter is raised so asto lift the pen free of the paper as indicated in broken lines in Fig.5. As member 35 is turned up so as to bring the middle of spring to(Fig. 4) above pivot 31, that also tends to maintain the pen M in suchraised position. The lead 5 may be clamped in the usual type of splitholder 26 which, in turn, is removably held in swinging member 36 bysetscrew 21, as best shown in Fig. 4. When 2'5 is loosened lead holder25 can be removed and pen M (Fig. 5) substituted for it, being alsoclamped in position by setscrew 2?, as shown in Fig. 4. The tensionspring til (Fig. 4) is connected at one end to hinged member 36 and atthe other to swinging member LlI which may be turned on its pivot 4 byhandle 42 through an angle of degrees, further swinging motionthereafter being prevented by stop 43. The purpose of this adjustment oftension on spring as, is to give a greater downward pressure to the leadI by turning member 4! into the position shown in Fig. 4 while a lesserpressure is given to pen 3! (Fig. 5) by turning said member ll up intothe position shown in Fig. 5 so as to diminish the tension on the spring.19 and also elevate its anchorage.

As indicated in Fig. '7 the entire marker mechanism carried by themember 32 may be shifted to the lefthand end of rod 22, the latter beingmoved to the left through the opening for it in the clamp member 9(looking at Fig. 2) When this is done, if the parts are so arranged thatthe point of the lead or pen is to the left of the axis of pivot 5(Fig. 1) the ellipse then traced will have its major axis running atright angles to that of any ellipse which would be traced with the partsin the position shown in Figs. 1 and 2.

To permit the movable, floating structure comprising crank 6, pivot 5,flat strip 2, clamp 9 and rod 22 to rotate easily in carriage 3, theball bearings 24, 24, are provided at either side of the latter asindicated in Fig. 2.

The mode of operation of the apparatus shown in Figs. 1 to 6 may beanalyzed as follows:

If pivot 5 and carriage 3 could be held stationary and disconnected fromlinks 8, 8b, revolution of crank 6 would then cause lead I to describe acircle about pivot 5, but so long as pin W connecting clamp 9 to theparallel motion mechanism is retained and carriage 3 is free to move onits guides i, the pivot W forms a shifting center of revolution for therigid swinging system of elements composed of lead I or pen 3! and saidelements, whenever the user pushes crank handle '5 around through aclosed loop path such as indicated by the arrows A, A, in Fig. 1.

Since pivot 5 moves to the right when crank handle 7 is pushed in thedirection of the upper arrows, A, A, and carriage 3 moves in the samedirection along guides 4, 4 (all as indicated in broken lines in Fig. 1)while lead I swings to the left as indicated by arrows B (and during thereturn half of the crank handle "I motion the reverse of the abovemovements occur) it will be seen that such to-and-fro motion of theshifting pivot center 5 will be progressively lengthening or shorteningthe effective radius of the would be circle (on one side or the other ofthe ellipse major axis L, L) which lead I may be considered as trying todescribe around such pivot 5 as a theoretical center, A at any onemoment. Consequently, such would be circle is thereby squeezed in ateach side (as an elastic ring could be deformed into an ellipse bysimultaneous opposing side pressures thereon); and the would be circlethereby becomes an ellipse B which is traced by the marker on the sheetof paper 25, beneath it.

The length of the major axis of such ellipse obviousy is twice thedistance from the point of lead I to pivot 5, while that of the minoraxis is twice the distance from said lead point to pivot W, since saidpivot always travels back and forth along the major axis of the ellipsebeing drawn, at right angles to the line of the guides 4, i. If themarker were shifted to: the other end of rod 22, as indicated in Fig.'7, the reverse would be true, the ellipse then traced being. of thetype indicated by arrows A, A.

When clamp 9 is adjusted on member 2 so that point W is beneath pivot 5,the rotation of handle '1 will cause lead I to describe a circle thediameter of which is determined by the distance of lead I from pivot ii.transition phase through which a series of ellipses like B of graduallydecreasing eccentricity might merge into another series like A ofgradually increasing eccentricity.

The center of the ellipse in either case coincides with the positionoccupied by the axis of pivot 5 when the parts are in the position shownin full lines in Fig. 1, that being the point at which the major andminor axes intersect. The broken Such circle would constitute the linesin Fig. 1 show the parts in a position as- 75 sumed when lead I is atsome point D in the ellipse periphery up to left of the major axis L, L.

The foregoing analysis makes it clear that in setting the preferred formof apparatus here shown rod 22 should be so adjusted in clamp member 9that the distance from lead I to W is half the minor axis of the desiredellipse, and thereafter clamp member 9 carrying rod 22 with it should beso adjusted on fiat bar 2 that the distance from lead I to 5 will equalhalf the major axis of such ellipse.

If the lengths and locations of the axes of any desired ellipse aregiven, the apparatus should be so placed that the medial line of guides4, 4' overlies the major axis while the pointer 30 rests on the minoraxis, and the castingsll, ll, then secured in that position by thumbtacks 23, 23. Thereafter the locations of the marker with reference topointer 39, and that of said pointer with reference to pivot 5, can beproperly adjusted as before explained.

Adjustments necessary to draw an ellipse conforming to other given datacan be worked out by the user from the principles of operationhereinbefore outlined, or by experiment.

Having described my invention, 1 claim:

In an apparatus for accurately tracing an ellipse the combination of amain frame provided with a rectilinear guide and means for fastening itin a position such that said guide will extend in parallel and fixedrelation to a plane surface on which such line is to be traced, amovable member provided at one point with pivotal means adapted to slidealong said rectilinear guide, and mechanism comprising a swingingstraight-line motion-producing device formed of a plurality of linkspivoted together and provided with elastic means for maintaining all thepivots thereof continually under a strain in the same general directionsufficient to overpower any normal operative strains in oppositedirections exercised thereon, said mechanism being pivoted at one pointon said guide and at another point pivoted to said movable member,combined with a marker adjustably mounted on said movable member andadapted to bear on and move over any surface on which said main frame issupported; whereby, when said frame is held in fixed relation to suchsurface with said marker bearing thereon and said movable member iscaused to revolve about the axis of said first mentioned pivotal means,the latter and said second point on said member at which it is pivotedto said straight-line motionproducing device are then severallycompelled to travel along their respective rectilinear paths, therebycausing said marker to trace the predetermined ellipse, or portionthereof, on such plane surface.

DAVID JOHN WITI-IERSPOON.

